1. Field of the Invention
The present invention relates to a semiconductor chip obtained by cutting, from a wafer, an element occupying a non-rectangular area. The present invention also relates to a module containing an element occupying a nonrectangular area. For example, the present invention relates to a chip and a manufacturing method thereof such as an arrayed waveguide grating chip, a manufacturing method thereof, and manufacturing a module containing an arrayed waveguide grating chip.
2. Description of the Related Art
As the volume of data to be transmitted increases, there is a corresponding demand for a larger transmission capacity in an optical fiber communications system. In addition, optical wavelength filtering is becoming increasingly important as an optical multiplexing/demultiplexing device for multiplexing and/or demultiplexing different wavelengths in Dense Wavelength Division Multiplexing (DWDM) systems. There are various types of optical wavelength filters. Among these, an arrayed waveguide grating has the desired wavelength characteristics such that a high extinction ratio is obtained in a narrow band region, and also features a filter device having multiple inputs and outputs. An arrayed waveguide grating is capable of multiplexing or demultiplexing signals, allowing a wavelength multiplexing/demultiplexing device can be easily constructed. Further, when the arrayed waveguide grating is constructed with quartz waveguides, the arrayed waveguide grating couples well with optical fibers and operates at small insertion loss, i.e., on the order of several dB (decibels). Due to these advantages, the arrayed waveguide grating is gaining recognition as a particularly important device among the optical wavelength filters.
FIG. 1 shows an overall structure of a related arrayed waveguide grating. An arrayed waveguide grating comprises one or plural input waveguides 12 formed on a substrate 11, a plurality of output waveguides 13, a channel waveguide array 14 wherein the respective arrayed waveguides are curved in a certain direction, each waveguide having a different curvatures. The arrayed waveguide grating further comprises an input side slab waveguide 15 for connecting the input waveguides 12 with the channel waveguide array 14, and an output side slab waveguide 16 for connecting the channel waveguide array 14 with the output waveguides 13. Multiplexed optical signals entering from the input waveguides 12 have their propagation paths expanded at the input side slab waveguide 15 before entering the channel waveguide array 14. In the channel waveguide array 14, the individual arrayed waveguides comprising the channel waveguide array 14 have mutually different optical path lengths. The individual arrayed waveguides are configured to progressively become either longer or shorter. Therefore, light propagating through the individual arrayed waveguides of the channel waveguide array 14 are imparted with predetermined phase differences before reaching the output side slab waveguide 16. As a result, light is focused (condensed) at mutually different positions on the interface of the output side slab waveguide 16 and the output waveguides 13 depending on wavelength. Since the output waveguides 13 are arranged at positions corresponding to different wavelengths, any given wavelength component can be taken from one of the output waveguides 13. Referring to FIG. 2, arrayed waveguide gratings 10 are commonly formed on a wafer comprising a silicon base or a quartz base. The wafer has a substantially disk-like shape, on which a plurality of the arrayed waveguide gratings 10 are formed and subsequently cut out into individual chips. For the cutting operation, it has been customary to use a technique called dicing, in which a saw blade is used to scan along predetermined cutting tracks. FIG. 2 shows how arrayed waveguide gratings 10 are laid out on a wafer for related cutting operations. In FIG. 2, the arrayed waveguide gratings 10 are cut along the cutting paths 22 and 23, respectively scribed in the X-axis and Y-axis directions at predetermined intervals, into individual chips, each having a rectangular shape.
As described above, it has been common cut a wafer using the cutting paths 22 and 23 to obtain individual chips of a rectangular shape. Cutting out individual rectangular shaped chips this way is efficient for ordinary integrated circuits, since the integrated circuit itself is formed into a rectangular shape.
The arrayed waveguide gratings shown in FIG. 1 are formed in an arcuate or a boomerang-like shape. Consequently, when arrayed waveguide gratings are cut out as rectangular chips as in the related art, wafer utilization efficiency is low since there is wasted space. Referring to FIG. 2, when a wafer 21 having a diameter of about 13 cm is used, only about 4 to 6 chips of the arrayed waveguide gratings can be obtained from one wafer 21. Thus, the arrayed waveguide gratings occupy a small area relative to the entire area of a wafer. FIG. 3 shows an example of 1xc3x97N splitters as another layout on a wafer. In this example, 1xc3x97N splitter chips 33 are cut out from a wafer 21 by using cutting paths 31 and 32. Although a 1xc3x97N splitter itself in this example is formed in a funnel shape obtained by dividing a rhombus in half, this is cut out in a rectangular shape, whereby only two chips 33 are cut out from one wafer 21. Thus, there is a similar problem low wafer utilization efficiency.
In view of the above, it is therefore an aspect of the present invention to provide a method of cutting a chip from a wafer such that a greater number of chips can be obtained from one wafer. In an exemplary embodiment, arrayed waveguide gratings having a non-rectangular area as a whole are provided on a wafer and cut therefrom, and a module containing an arrayed waveguide grating is manufactured.
To solve the above problem, a chip of the present invention is obtained by cutting it from a wafer along its contour of a concave shape recessed in one direction. An arrayed waveguide grating is provided on the chip, and the shape of the chip is determined on the basis of the shape of the arrayed waveguide grating. The chip comprises reinforcement means mounted on at least a portion of the chip so as to reinforce the chip. It is preferable that the reinforcement means are mounted on a narrow part of the chip. The reinforcement means is preferably a copper plate having a shape identical to the chip. The reinforcement means may be a rectangular copper plate formed with such a size as to entirely surround the chip. Moreover, a chip of the present invention comprises a first chip obtained by cutting it from a first wafer along its contour of a concave shape recessed in one direction, a second chip obtained by cutting it from a second wafer along a contour that is identical to the contour of the first chip and combining means for combining the first chip with the second chip. The combining means can be an adhesive.
A wafer of the present invention includes a plurality of chips obtained by cutting along the contour of a concave shape recessed in one direction. The concave shapes of adjacent chips are at least partially overlapped with each other. The plurality of chips have the same shape. The shape is an arcuate shape having two curved-line portions convexed in the same direction. The chips are arranged at a predetermined spacing and respective end portions thereof are connected to two mutually parallel straight lines. Alternatively, the shape is a funnel shape obtained by dividing in half a rhombus in which two curved-line portions are convexed in a direction moving away from each other. The chips are arranged at a predetermined spacing and the respective end portions thereof are connected to two mutually parallel straight lines.
Another aspect of the present invention provides a module comprising a chip cut from a wafer along a contour of a concave shape that is recessed in one direction, a box comprised of an upper casing and a lower casing for accommodating the chip, and buffer agents provided in the box. The module further comprises a temperature detecting means that detects the temperature inside the casing and controlling it. Moreover, the module comprises a support body mounted on the chip for supporting the chip and a spring part provided in the box for mounting the support body. The support body is preferably a metal plate.
Another aspect of the present invention provides a chip manufacturing method, wherein the method forms, on the same wafer, a plurality of elements that are bounded by their respective contours. The contours of the elements comprise a concave shape recessed in one direction. The elements are cut from the wafer to obtain chips comprising an individual element.
A laser beam is used to cut the wafer along the contours to obtain individual element chips. The cutting step may use an ultrasonic vibration tool adapted to match the shape of the contours of the respective elements. The cutting out step may use hydraulic pressure to obtain the chips having an individual element. Dicing is used to cut the straight-line portions of the chip contours. The chip manufacturing method further comprises mounting a plate on at least a part of the chip for reinforcing the chip. Moreover, the chip manufacturing method cuts out a first chip from a first wafer along the contour of its concave shape recessed in one direction, and cuts out a second chip from a second wafer having the same shape as that of the first chip and bonding together the first and second chips. The bonding step bonds together the first and second chips using an adhesive.
According to the present invention, the number of chips that can be obtained from one wafer is increased because individual chips are formed in a concave shape wherein unnecessary portions are removed.